1. Field of the Invention
The present invention relates to a display device, and more particularly, to a 2D/3D switchable liquid crystal lens (LC lens) unit for use in a display device.
2. Description of Prior Art
Real-world images are perceived by the human eye, and further, so-called three-dimensional (3D) images are perceived by the human brain depending on an apparent displacement of an object viewed along two different lines of sight. Such a displacement or a spatial difference is called parallax. A so-called 3D display device, simulating human vision to form different viewing angles, is capable of conveying 3D images to the viewer. The 3D display device produces two different 2D images with parallax, one for the viewer's right eye and the other for the left eye. Afterwards, the viewer's brain perceives these two different 2D images as a 3D image.
Nowadays, there are two types of 3D display devices in general, auto-stereoscopic displays and stereoscopic displays. A user of an auto-stereoscopic display can see three-dimensional images without wearing special type glasses. As for a user of a stereoscopic display, he/she has to wear special type glasses to see three-dimensional images. A commonly seen auto-stereoscopic display is divided into two types: slit grating auto-stereoscopic displays and microlens array auto-stereoscopic displays. The theorem of slit grating auto-stereoscopic displays lies on that a user sees parallax images through both eyes based on an opaque parallax barrier, and the parallax images is perceived as stereoscopic view in the brain. As for microlens array auto-stereoscopic displays, an LC lens unit acts as a lenticular lens and is attached onto an LC panel. The LC lens unit is fitly made of a single refractive index microlens array and a birefringence index microlens array fitly. The birefringence index microlens array is made of liquid crystals. The variations of the electric field applied on the birefringence index microlens make LC molecules adjust the alignment and the refractive index. The horizontal direction of LC molecules becomes the vertical one, and the ordinary refractive index no becomes the extraordinary refractive index ne. In this way, the light emitted to the lens unit has various emitting directions owing to variations of the refractive index of the birefringence index microlens. According to this theorem, the user can see light with two different types of refractive angles, which makes it possible to switch between 2D/3D images. However, a traditional lens unit structure is that two-layer control electrodes are individually disposed on the upper and lower sides of the birefringence index microlens. The two-layer control electrodes have a driving voltage difference which generates an electric field. The electric field adjusts the horizontal direction of the LC molecules into the vertical direction. Generally speaking, the driving voltage difference goes up to 5 volts or more. So, to produce a lens unit with low driving voltage for switching between 2D/3D images will meet ecological demands greatly.